1. Field of the Invention
The present invention relates to a biopsy apparatus and a biopsy method for calculating a three-dimensional position of a region to be biopsied (hereinafter referred to as a “biopsy region”) of an object to be examined, based on at least two radiographic images obtained by irradiating the object with radiation from directions that are different from each other, then moving a biopsy needle to the biopsy region based on the calculated three-dimensional position, and removing a tissue sample from the biopsy region.
2. Description of the Related Art
Heretofore, biopsy apparatus have been developed in the art for removing a tissue sample from a biopsy region of an object to be examined (e.g., an inflicted region of a breast of a subject) and examining the tissue sample to perform a disease diagnosis of the subject. In order to identify the position of the biopsy region, the biopsy apparatus incorporates a radiographic image capturing apparatus, which captures a plurality of radiographic images under a stereographic image capturing mode by applying radiation to the object from directions that are different from each other. The three-dimensional position of the biopsy region is specified using the captured radiographic images. Then, a biopsy needle is moved toward the biopsy region based on the specified three-dimensional position, and a tissue sample is removed from the biopsy region.
Techniques for specifying the position of a biopsy region using a plurality of radiographic images, techniques for removing a tissue sample from the biopsy region, and techniques concerning radiographic image capturing apparatus incorporated in biopsy apparatus have been proposed or disclosed in Japanese Patent No. 3668741, Japanese Laid-Open Patent Publication No. 2001-504002 (PCT), Japanese Laid-Open Patent Publication No. 10-201749, and Japanese Laid-Open Patent Publication No. 2002-186623.
It is proposed in Japanese Patent No. 3668741 that a scintillator of a radiation detector converts radiation into light, and that a CCD array converts the light into a radiation image.
It is proposed in Japanese Laid-Open Patent Publication No. 2001-504002 (PCT) that the cassette of a radiation detector is separated from a radiographic image capturing apparatus when the cassette is not in use.
It is proposed in Japanese Laid-Open Patent Publication No. 10-201749 to acquire two radiographic images by irradiating a phantom having a marker, which is disposed in a known position, with radiation at two angles, whereby a calculating algorithm for identifying the position of a biopsy region is modified based on the acquired two radiographic images and the position of the marker of the phantom.
Japanese Laid-Open Patent Publication No. 2002-186623 discloses that a biopsy needle is inserted obliquely into a biopsy region in order to remove sample tissue therefrom.
In a stereographic image capturing mode that applies radiation to an object from different directions, since plural radiographic images need to be captured in order to identify the position of the biopsy region, the dose of radiation applied to the examinee is increased. Further, the time required to examine the biopsy region depends on the skill of the doctor or technician who uses the biopsy apparatus. Therefore, if the doctor or technician who uses the biopsy apparatus is not skilled, then the examination process becomes time-consuming, and tends to hold the object for a long period of time. Consequently, it would be desirable to reduce the number of radiographic images that are captured, for thereby minimizing the dose of applied radiation and shortening the time required for the examination process.
According to Japanese Patent No. 3668741, since a CCD array is used to capture a radiographic image of an object, the object is exposed to radiation at all times, and hence the applied radiation dose is high. According to Japanese Laid-Open Patent Publication No. 2001-504002 (PCT), since eight to ten radiographic images need to be captured in order to identify the position of the biopsy region, the number of captured radiographic images cannot be reduced, and further, the applied radiation dose cannot be reduced. Japanese Laid-Open Patent Publication No. 10-201749 and Japanese Laid-Open Patent Publication No. 2002-186623 do not propose any techniques or methods aimed at reducing the number of radiographic images required to be captured so as to reduce the applied radiation dose. In addition, attempts to shorten the time required for the examination process by reducing the number of captured radiographic images have not been proposed in Japanese Patent No. 3668741, Japanese Laid-Open Patent Publication No. 2001-504002 (PCT), Japanese Laid-Open Patent Publication No. 10-201749, or Japanese Laid-Open Patent Publication No. 2002-186623.
Japanese Laid-Open Patent Publication No. 2001-504002 (PCT) discloses that the angle of a radiation source with respect to the perpendicular axis of a radiation reception surface of the radiation detector is set to ±15° in a stereographic image capturing mode. The angle of the radiation source is set this way because if a scout image capturing mode is performed to irradiate the object with radiation emitted from a radiation source disposed on the perpendicular axis (0°), then the biopsy needle also is imaged in overlapping relation to the biopsy region in the radiographic image captured in the scout image capturing mode, thus making it impossible to identify the position of the biopsy region. According to Japanese Laid-Open Patent Publication No. 2001-504002 (PCT), in order to prevent the biopsy needle from being imaged, the biopsy region is imaged while capturing two radiation images, i.e., when the radiation source is positioned at an angle of +15° and an angle of −15° respectively, whereby the position of the biopsy region is identified using the two captured radiographic images.
In the scout image capturing mode, scattered rays of radiation, which are generated when radiation is applied to the object, are removed by a grid. The grid is of a structure having an alternate pattern made up of one material, which is permeable to radiation, and another material, which absorbs radiation. The grid is disposed near the radiation reception surface of the radiation detector. In the stereographic image capturing mode, since the angle of the radiation source with respect to the perpendicular axis of the radiation reception surface of the radiation detector is set to ±15°, which differs from the angle of the radiation source used in the scout image capturing mode, the radiation required to capture radiation images tends to be absorbed by the grid. Consequently, the grid cannot be used in the stereographic image capturing mode. As a result, radiation images captured in the stereographic image capturing mode may possibly be of low quality, due to such scattered radiation.